An adhesive tape and an adhesive sheet are obtained by forming an adhesive on a surface of a substrate and are usually stored after taking up in a roll form. In that case, the back surface of the substrate is generally coated with a release agent to protect the adhesive surface of the adhesive tape or adhesive sheet. When using the adhesive tape or adhesive sheet, it can be easily unwound. Alternatively, the adhesive surface is covered with a separate substrate coated with a release agent, thereby to protect the adhesive surface.
Various types of release agents have been known. Particularly, a release agent having a long-chain alkyl group (long-chain alkyl-based release agent) is useful in the electronic industry because it is comparatively cheap and is less likely to cause contamination.
One example of the long-chain alkyl release agents is disclosed in the pamphlet of International Publication WO 01/64805 and/or KOKAI (Japanese Unexamined Patent Publication) No. 2001-240775. Each of these long-chain alkyl release agents is an acrylic release agent comprising a product obtained by irradiating an acrylic release agent precursor, which contains a poly(meth)acrylate ester and has a storage elastic modulus of 1×102 to 3×106 Pa at 20° C. and a frequency of 1 Hz, with ultraviolet radiation, said acrylic release agent having a contact angle of 15° or more with a mixed solution of methanol and water (volume ratio of 90/10) having a wetting tension of 25.4 N/m. This acrylic release agent has comparatively high adhesion with a substrate made of polyethylene terephthalate after applying on the substrate. This acrylic release agent can maintain a comparatively low peel force from a pressure-sensitive adhesive such as acrylic pressure sensitive adhesive even when exposed to high temperature. Furthermore, this acrylic release agent substantially has no influence on the residual adhesion of the adhesive.
As is apparent from the above description, the acrylic release agent described above is prepared by passing through the step of irradiating the acrylic release agent precursor with ultraviolet radiation. However, the ultraviolet irradiation dose required in this step varies widely depending on the composition of the acrylic release agent precursor. When the composition which requires a small dose to form a release agent is compared with the composition which requires a large dose, the dose varies sometimes by 3 to 5 times.